Field of the Invention
The invention relates to the field of aviation, more specifically—to devices for determining air vehicle flight parameters or wind tunnel flow parameters, and even more specifically—to measuring three components of an air speed vector and a static pressure.
Description of the Related Art
The air pressure probe (APP) is the most important component of the airflow parameter measurement system. The information obtained therefrom is processed further to determine the values of flight altitude and speed to be displayed in the cockpit of a flying vehicle for its crewmembers.
Existing currently are air probes with a number of configurations:                those implemented in the form of elongated axially symmetrical bodies with a head part in the form of a hemisphere, a cone or an ogive, and with several intake holes on the head part, which are connected via pneumatic channels to couplers (A. N. Petunin, Methods and techniques for measuring gas flow parameters.—M.: Mashinostroenie, 1972, pp. 20-21, 118-125);        those with the housing in the form of a cylinder rod with a circular section and with intake holes, located on a lateral surface of the housing and connected via pneumatic channels to couplers (A. N. Petunin. Methods and technique of measuring gas flow parameters, M., Mashinostroenie, 1972, pp. 88-100);        those with the housing in the form of a cylinder rod, with a bottom cross section, and with intake holes located both on the front windward part of the housing, and on the bottom cross section (M. A. Golovkin, V. I. Guskov, A. A. Efremov, Air pressure probe, RU 1723879 of Mar. 11, 1997.        
The main disadvantage all those and similar APPs have is the impossibility of measuring parameters of a three-dimensional gas flow.
The closest analog, considering the operations to be carried out and the technical solution implemented, is the APP, which has a spherical head part with intake holes located thereon and connected via pneumatic channels to couplers, and a straight or L-shaped support with a circular section (Vijay Ramakrishnan and Othon K. Rediniotis. Development of a 12-Hole Omnidirectional Flow-Velocity Measurement Probe, AIAA Journal, Vol. 45, No. 6, June 2007, pp. 1430-1433).
This APP has the following disadvantages.                the measurement range is limited by Reynolds numbers and flow speed;        the surface quality of the head part of the APP should meet tough requirements;        complicated design;        limited area of the practical applicability of the APP.        
The abovementioned disadvantages result from the following.
1. It is known (K. P. Petrov, Simple Shape Body Aerodynamics. Scientific publication—M.: Factorial Publishing House, 1998, pp/58-68), that increasing the Reynolds number results in flow-around modification of a smooth sphere from subcritical to supercritical resulting in sharp shift of the position of the flow break-away point. Coming with that is a sharp (by speed and, respectively, Reynolds number) change of pressure distribution over the smooth sphere surface. This results in the need to account for the dependence of the flow-around nature on the Reynolds number, when simulating the APP mathematically, expanding the database and introducing certain corrections. This, correspondingly, complicates further calculations of the component vector of speed and angle of attack, based on the math model created. To eliminate this problem, the head part of the prior art is designed as a sphere with small diameter (d=6.35 mm and d=9.53 mm) (www.aeroprobe.com), resulting in the entire operational range of speeds (V<320 m/s for the sphere with d=6.35 mm and V<70 m/s for the sphere with d=9.53 mm, ibid.), as well as Reynolds numbers, associated with the head part flow-around, to have the subcritical nature, and the boundary layer on its surface to be laminar. However, experiment results displayed on FIG. 10 and reflected in (K. P. Petrov, ibid.), reveal that under subcritical flow-around of a smooth sphere, and with the Reynolds number Re=85000, the laminar boundary layer separation takes place when the angle φ≈77° (wherein φ is the angle between radius vectors of a stagnation point and a boundary layer separation point). As result, measuring arbitrarily directed vector of speed required 18 holes for pressure measurement to be made on the surface of the head part of the APP, distributed evenly and symmetrically, each of the holes being connected to a coupler via a pneumatic channel, thus making the APP design more complicated, and increasing the APP weight. Using less holes, distributed evenly, for this design of APP, generally, is not acceptable, for this may result in a situation (with stagnation point matching one of the intake holes), where the air pressure would be conclusively measured with only one hole, the rest being at the separation zone. Besides, the dimensions of the head part and the support part attached thereto would necessitate using pneumatic channels with a very small inner diameter. Together with the long length of a pneumatic channel (for the head part with d=9.53 mm (www.aeroprobe.com), the full length l with the L-shaped support is 357 mm), it leads to significant delays in the signal passage, and, thus, to delay in obtaining measurement results.
2. It is commonly known, that the need to guarantee subcritical flow-around of the sphere and laminar boundary layer on its surface (without forced laminarization by dedicated devices, which would be hard to use due to small dimensions of the APP) toughens requirements to the sphere surface smoothness. Any irregularities or unsmooth spots on the surface result in boundary layer turbulence which leads to turning subcritical flow-around into supercritical one (for example, see Prandtl L.—Tietjens O. Hydro- and aeromechanics—ONTI NKTP USSR, Moscow, Leningrad, 1935, pp. 41-45, 52-54), resulting in significant distortion of the total flow-around picture against the one, the math simulation model of flight parameter calculation was developed for.
3. The abovementioned APP features result in limitations on practical usability of the prior art probe, which may only be used in wind tunnels and test benches. Using it in real flying vehicles is impossible, because, due to small dimensions, it cannot host a number of systems, which are obligatory for the use on APPs mounted on real flying vehicles, in particular, heating systems, systems for condensed water vapor removal from pneumatic channels etc. Making the APP larger is impossible either, because this, due to restrictions imposed on Reynolds number to keep flow-around subcritical, would narrow the range of measurable speeds down to unacceptable level (V<30 m/s).